Reduced bandwidth processing for ultrasonic image conversion

ABSTRACT

Disclosed is an ultrasonic, image conversion, high definition sonar having a multitude of transducer channels employing improved signal processing in each channel to reduce video bandwidth and switching speed requirements. Signal processing is characterized in each of the multitude of channels by detecting and holding the peak return from a transmit pulse for the remainder of the pulse project period, then holding that peak value for the subsequent pulse project period, during which time the value may be multiplexed for conversion to video signals for a CRT display, or may be applied to elements of an LED array.

United States Patent [191 Rolle llama. 29, W74

rim ry Etfl inekg fitBa rs REDUCED BANDWIDTH PROCESSING FOR A 7 i w HULTRASONIC IMAGE CONVERSION Attorney, Agent, or F irm-Richard S.Sciascia, Don [75] Inventor: Albert L. Rolle, Lynn Haven, Fla. igfy iDavld [73] Assignee: The United States of America as 57 AB representedby the Secretary of the SACT N W hi D Disclosed is an ultrasonic, imageconversion, high definition sonar having a multitude of transducer chan-[22] Filed 1972 nels employing improved signal processing in each [21]App], N 297,574 channel to reduce video bandwidth and switching speedrequirements. Signal processing is characterized in each of themultitude of channels by detecting and 340/3 lgg holding the peak returnfrom a transmit pulse for the s l u s I s I s s I n [58] Fm Search 340/55 3 6 that peak value for the subsequent pulse project pe- 43/16 17riod, during which time the value may be multiplexed for conversion tovideo signals for a CRT display, or [56] References Cited may be appliedto elements of an LED array.

UNITED STATES PATENTS 3,7l7,843 2/1973 Farrah et a]. 340/1 R 8 2 Dmwmgfigures 7?? A an m /\R A .W.V r f! MDULEU "7"" MULTICHANIJH BANDWIDTH "WUL LE k i RECEIVER 56 SIGNAL 3 GATES .v Lu, PROCESSOR l 2o 1 T/RSWITCHES TRANSMITTER ifig (RE'S'EI: (CLOEK) l8 "I :5 4 (TRANSMIT)(PROGRAM) d 1 ZBZI C J F 2 l2 l2 1 FLJNCTlON GENERATOR I (SIR 1 50TRABJDUCER AER Ad O (SYNC) i as 64 x s v SWEEP GENERATORS (X) (Yl 50W25? 62 T' ,LMQL

REDUCED BANDWIDTH PROCESSING FOR ULTRASONIC IMAGE CONVERSION STATEMENTOF GOVERNMENT INTEREST The invention described herein may bemanufactured and used by or for the Government of the United States ofAmerica for governmental purposes without the payment of any royaltiesthereon or therefor.

BACKGROUND OF THE INVENTION This invention relates to ultrasonic imageconversion as used in high definition sonar systems, and moreparticularly, to improvements in video processing therein which permitcathode ray tube visual displays and brighter light emitting diodedisplays, when used.

The carrying out of various underwater tasks by divers is often hinderedby turbid water conditions which render a diver effectively blind if hemust rely on an un aided view through his faceplate or mask. Lights andother optical aids are ineffective in a turbid environment because ofbackscatter from particulate matter. Chemicals and mechanical envelopescan be effective to clarify turbid water, but are subject to variouslimitations which restrict their use.

Because ultrasonic energy propagation is relatively unaffected by turbidconditions of water, efforts have been directed to development ofultrasonic means of generating or enhancing images of objects within theworking range of a diver to enable him to carry on tasks such as hullinspection and repair, detection of various objects, rescue, and thelike.

Patent application Ser. No. 296,500, filed in the U. S. Pat. Office onOct. 4, 1972, and entitled Sonar Image Converter, by A. L. Rolledescribes in considerable detail a diver or swimmer carried ultrasonicimageconversion visual display system which goes far toward overcomingthe problems of viewing objects in turbid water. In that system, pulseduntrasonic energy is transmitted and target reflected energy is focusedon an array of transducer elements located at the focal plane of anultrasonic lens. The output of each element of the transducer array isamplified, band limited, and envelope detected in a separate channel.The detected output signal of each transducer element channel isprocessed and used to control energization of an LED (light emittingdiode) in an array of LEDs corresponding in number and arrangement tothe transducer array. The transducer and LED arrays are mounted on acommon shaft for synchronized rotation and scanning of a viewing zone.The resulting visual display is an image of the target of interestrather than an indication of bearing and range, as in conventionalsonar.

For successful direct viewing of the LED array, it is necessary thatenergization of the individual LEDs be for a long enough period, say 500psec or longer, to provide adequate light to stimulate the eye. Theenvelope-detector output in the above system is approximately equal tothe width of the projected pulse and typically ranges from 50 to 300usec. Accordingly, the mentioned signal processing following theenvelope detector of each channel serves to detect the peak value of theenvelope and hold it for a period inversely proportional to the range ofthe target of interest or at least for some minimum period which wouldassure visual stimulation by the LED.

Now in some circumstances it would be desirable to utilize a CRT(cathrode ray tube) display in an ultrasonic image conversion sonarrather than an LED array. These circumstances would include situationswhere power and weight factors are not as restrictive as in the case ofswimmer/diver use, for example, when mounted on a submersible vessel.With a CRT display, the output of each envelope detector would besequentially gated to a single video amplifier by an analog multiplexer.The video amplifier would drive the Z or amplitude axis of the CRT. Thenumber N of transducer elements can vary from approximately 30, as inthe mechanically scanned array of the co pending application, topossibly 10,000 elements in an extensive electronically scanned array.For use with a CRT it is desirable to sample all of the envelopedetector outputs at least once for each projected pulse. If done in aperiod corresponding to a projected pulse width PW, the sampling timeper sample then would be PW/N. For even small transducer arrays, thesampling time per sample would be extremely short and would require highpower, wide-band sampling gates, drive logic, and CRTs. Sampling at highspeeds also introduces significant errors due to the spikes generated inthe signal channel by the rapidly changing drive logic voltages.

For extensive arrays with thousands of transducer elements, signalprocessing as used heretofore would require long projected pulse widthsto facilitate within pulse scanning. Long pulse widths are undesireablein turbid water, where the need for ultrasonic imaging is the greatest,as the contrast between the target echo and volume reverberationdecreases as PW increases.

SUMMARY OF THE INVENTION With the foregoing in mind, it is a principalobject of this invention to provide an improved ultrasonic imageconversion sonar which is particularly useful in turbid waterconditions.

Another object of the invention is to provide an image conversion sonar,wherein a cathode ray tube can be utilized as the visual display means.

Still another object is the provision of a high definition sonar havinga transducer array in which the transducer elements may number in thethousands.

Yet another object is to provide an improved image conversion sonaremploying signal processing means, such that elements of an LED displaywill be excited for a period which is independent of the range to thetarget, thereby increasing the apparent brightness of the display forvery short pulse width projections.

As another object, the invention aims to provide an improved sonarsystem having one or more of the foregoing characteristics and whichutilizes improved signal processing in each transducer channel wherebyweight, power, and most importantly, bandwidth'requirements aresubstantially reduced in the generation of images from relatively shortpulse width ultrasonic projections.

Other objects and many of the attendant advantages will be readilyappreciated as the subject invention be comes better understood byreference to the following detailed description, when considered inconjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS 7 FIG. l is a diagrammaticillustration in block form of an ultrasonic, image conversion, highdefinition sonar system embodying the invention; and

FIG. 2 is a diagrammatic illustration, in greater detail, of the signalprocessing portion of the system of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1, the generalorganization of an exemplary ultrasonic image conversion sonar systememploying the invention comprises a transducer array 10, including anumber of transducer elements 12. The transducers 12, which may numberfrom approximately 30 to 10,000 or more depending upon the use to whichthe system is put, are connected as shown by lines 14 to transmit andreceive switches 16. The latter serve in the usual manner to directtransmission pulses received via lines 18 from a transmitter 20 to theelements 12, and to direct return signals detected by the elements 12 toappropriate channels of a multi-channel receiver 22 via correspondinglines 24.

The transmitter 16 and the receiver 22 are under the control of a systemfunction generator 28 for transmission, range gate, and gain controlfunctions as indicated by lines 30, 32, and 34, respectively. Theoperation of the system as described thus far may be regarded as thesame as in the above mentioned application, to which reference may behad for further details.

The outputs of the channels of the receiver 22, indicated by lines 36are in the form of signal envelopes 38, each representative of thereturn from a corresponding transducer element within the reception timedictated by the range gate.

The receiver outputs on lines 36 are applied to corresponding channelsof a reduced bandwidth signal processor 40, the construction, purposesand functions of which will be described in more detail with referenceto FIG. 2, as this specification proceeds. Suffice it to say for themoment that the envelope detected signals 38 are processed in theprocessor 40, under the control of signals represented by lines 42 and44 from the function generator, to generate for each channel a signallevel representative of the peak response of the associated transducer,which signal levels are available at the outputs 46 of the processor forsufficient time to be individually sampled by multiplexer gates 48 inaccordance with an order of succession determined by a multiplexer logic50. The latter may take various forms but conveniently comprises shiftregister means having outputs 52 under the program control of thefunction generator 28, as shown byline 54.

The sampled outputs of the multiplexer gates 48 are summed on line 56for application-as the input to a video amplifier 58, the output ofwhich on line 60 drives the Z axis (brightness) of a cathode ray tubedisplay 62. Sweep generators 64 are provided for developing a suitableraster on the CRT display at a frame rate determined by a sync signaloutput 66 of the function generator 28. i

Referring now to FIG. 2, the'signal processor construction and operationwill be described in more detail, the description being confined to theoperation of one channel with'the understanding that it applies as wellto the numerous parallel channels which would be employed. The incomingdetected envelope on line 36 is applied to an operational amplifier 70having its ref-' erence side connected through a capacitor 72 to ground,and having its output 74 connected through a diode 76 and line 78 to thereference side, as well as to the input of a buffer amplifier 80. Thisamplifier 70, capacitor, diode configuration will be recognized as apeak detection and hold circuit.

A transistor 82 has its emitter-collector circuit connected across thecapacitor 72, and its base connected to receive a reset pulse 84 vialine 42. In this regard, the reset pulse 84 is conveniently generatedwithin the function generator 28 by a delay means in the form of asingle shot multivibrator, or one-shot, 86. The oneshot 86 is triggeredby the negative going characteristic of each of a train of clock pulses88 on line 90.

The clock pulses 88 are also applied via line 44 to a gate means,conveniently in the form of a field effect transistor 92 which, whenrendered conductive by the positive clock pulses, transfers the outputof the buffer amplifier to the input of an operational amplifier 94 andto a capacitor 96. The gate 92, amplifier 94, and capacitor 96 will berecognized as constituting a sample and hold circuit.

The output signal level line 46 from the sample and hold circuit isgated by a transistor 100 to the video amplifier input line 56 inresponse to a control pulse 102 from the multiplexer logic 50. In thisregard, it should be noted that transistor 100 is only one of theplurality of gating transistors corresponding to the plurality ofchannels in the system and that point 104 is a summing node for theplurality of channel sample and hold levels gated by these transistors.

MODE OF OPERATION In the operation of the system, an isonifying pulsehaving a width of say 10 usec to I00 p.860 is projected every T seconds,the period T being referred to as the project pulse period. The pulseprojection is conveniently under the control of clock signals 88, whichclock signals are also applied as shown by lines and 44 to the one-shot86 and to the gating transistor 92. Consider the pulse project period Tto be equal to twice the maximum range of interest in feed divided bythe velocity of sound c in the medium concerned, usually sea water. Forexample, if the maximum range of interest for a particular applicationis 10 ft., T is approximately 4 msec.

At a time during the period T, depending upon the range of a target ofinterest within 10 feet, a detected envelope will arrive on line 36 andwill be peak detected and held by the action of amplifier 70, capacitor72, and diode 76. At the end of the period T, the gating transistor 92is rendered conductive for a period sufficient to sample the voltagelevel of buffer amplifier 80 which, of course, represents the peakdetected and held value, and store it in the hold circuit formed bycapacitor 96 and amplifier 94. As the last mentioned clock pulse 88 goesnegative, the one-shot 86 is fired causing it to provide the pulse 84whichresets the peak detect and hold circuit in readiness for the nextreturn signal.

The response time of the one-shot 86 conveniently inrelease that valueto the video amplifier input line 56.

Keeping in mind that the preferred projected pulse width is on the orderof usec and that the project pulse period T is on the order of 4 msec inthe example given, the described processing gives an increase in time bya factor of 400 during which N channels can be sampled by the multiplexlogic for CRT presentation. Accordingly, this allows employing ofmicrowatt logic and analog gates and, because of the relatively lowswitching speeds, feed through of the logic switching voltages into thesignal channels is significantly re duced.

If an LED display is desired where the brightness of the display isassured for all ranges, rather than having the brightness inverselyproportional to range as in the aforementioned application, the outputof each channel on line 46 may be applied to the corresponding LED.

Obviously, other embodiments and modifications of the subject inventionwill readily come to the mind of one skilled in the art having thebenefit of the teachings presented in the foregoing description and thedrawing. It is, therefore, to be understood that this invention is notto be limited thereto and that said modifications and embodiments areintended to be included within the scope of the appended claims.

What is claimed is:

ll. An ultrasonic, image conversion, high definition sonar systemcomprising in combination:

function generator means for providing control signals including clocksignals, each representing a pulse project period, and reset signals;

transducer means, comprising an array including a plurality ofindividual transducer elements, for periodically projecting ultrasonicenergy pulses of predetermined width and responsive to ultrasonic energyreflected from a target within a predetermined range of interest togenerate electrical echo signals corresponding thereto;

receiver means for detecting said echo signals, and

comprising a plurality of channels for generating envelope signalscorresponding to echo signals from each of said transducer elementssignal processing means comprising a plurality of channels, eachconnected to receive the output of one of said receiver channels, forgenerating, from said envelope signals, output signal levels;

each channel of said signal processing means comprising peak detect andhold means for detecting the peak value of an envelope signal occurringin a particular pulse project period and for holding said peak valueduring the remainder of that pulse project period, sample and holdmeans, responsive to said clock signals, for sampling said peak value atthe beginning of the next pulse project period and for holding said peakvalue as one of said output signal levels until the beginning of thefollowing pulse project period, and means for resetting said peak detectand hold means after said sampling of said peak value; and

visual display means responsive to said output signal levels to producecorresponding emissions of eye stimulating light.

, 6 2. A sonar system as defined in claim 1, and wherein:

said display means comprises cathode ray tube means.

3. A sonar system as defined in claim 2 and further comprising:

video amplifier means for driving said cathode ray tube means; and

multiplexer means including logic means and multiplexer gate meansresponsive to said logic means for coupling said output signal levels ofsaid signal processor channels to said video amplifier means inaccordance with a predetermined program.

4. A sonar system as defined in claim l and wherein:

said peak detect and hold means of each signal processor channelcomprises an operational amplifier, capacitor, and diode combination,wherein the peak input signal is stored on said capacitor, andtransistor means for discharging said capacitor to reset said peakdetect and hold means; and

said function generator means comprises means for generating a resetpulse following each of said clock pulses, said transistor means beingrendered conductive by said reset pulse.

5. A sonar system as defined in claim 4, and wherein:

said sample and hold means of each signal processor circuit comprises aswitching transistor, capacitor, and operational amplifier combination,and buffer amplifier means coupling said peak detect and hold means tosaid sample and hold means; and said switching transistor beingoperative in response to said clock signals to apply the output of saidbuffer amplifier means to said capacitor and operational amplifier ofsaid sample and hold means. 6. A sonar system as defined in claim 5, andwherein said display means comprises cathode ray tube means.

7. A sonar system as defined in claim 6, and further comprising:

"video amplifier means for driving said cathode ray tube means; and

multiplexer means, including logic means and multi plexer gate meansresponsive to said logic means, for coupling said output signal levelsof said signal processor channels to said video amplifier means inaccordance with a predetermined program.

8. In an ultrasonic, image conversion sonar system of the type includinga source of clock signals representing the end of one pulse projectperiod and the start of another, a plurality of transducers, andreceiver means having a plurality of corresponding channels forgenerating echo envelope signals, reduced bandwidth signal processingand display apparatus comprising:

a plurality of echo envelope peak detection and holding means forproviding a peak voltage level representative of the peak return signalin each of said channels during a first predetermined period in whichechoes may be received from a given pulse transmission, said peakdetection and holding means each comprising a storage capacitorconnected to receive and store said peak voltage level and transistormeans connected to said capacitor for discharging thereof in response toreset signals;

reset signal generating means connected to said transistor means andresponsive to said clock signals for generating said reset signals;

a plurality of sample and hold means, each connected by a bufferamplifier means to one of said peak de- 7 8 tection and holding means,for sampling the voltvideo amplifier means connected to the cathode ofage level stored on said storage capacitors in resaid cathode ray tubemeans and responsive to said sponse to said clock signals, and forproviding corcorresponding voltage levels from said sample andresponding voltage levels for a second predeterhold means, when appliedthereto, to modulate the mined period following said first predeterminedpeintensity of said visible display; and riod, said sample and holdmeans each comprising multiplexer means, including logic means andmultia switching transistor, capacitor, and operational plexer gatemeans, said multiplexer means being amplifier combination; connectedbetween said sample and hold means cathode ray tube means for generatinga visible disand said video amplifier means so as to apply said play ofsaid peak return signals; 10 corresponding voltage levels to said videoamplifier sweep generating means, connected to said cathode means inaccordance with a predetermined pro:

ray tube means, for causing a raster to be traced gram. thereby;

1. An ultrasonic, image conversion, high definition sonar systemcomprising in combination: function generator means for providingcontrol signals including clock signAls, each representing a pulseproject period, and reset signals; transducer means, comprising an arrayincluding a plurality of individual transducer elements, forperiodically projecting ultrasonic energy pulses of predetermined widthand responsive to ultrasonic energy reflected from a target within apredetermined range of interest to generate electrical echo signalscorresponding thereto; receiver means for detecting said echo signals,and comprising a plurality of channels for generating envelope signalscorresponding to echo signals from each of said transducer elementssignal processing means comprising a plurality of channels, eachconnected to receive the output of one of said receiver channels, forgenerating, from said envelope signals, output signal levels; eachchannel of said signal processing means comprising peak detect and holdmeans for detecting the peak value of an envelope signal occurring in aparticular pulse project period and for holding said peak value duringthe remainder of that pulse project period, sample and hold means,responsive to said clock signals, for sampling said peak value at thebeginning of the next pulse project period and for holding said peakvalue as one of said output signal levels until the beginning of thefollowing pulse project period, and means for resetting said peak detectand hold means after said sampling of said peak value; and visualdisplay means responsive to said output signal levels to producecorresponding emissions of eye stimulating light.
 2. A sonar system asdefined in claim 1, and wherein: said display means comprises cathoderay tube means.
 3. A sonar system as defined in claim 2 and furthercomprising: video amplifier means for driving said cathode ray tubemeans; and multiplexer means including logic means and multiplexer gatemeans responsive to said logic means for coupling said output signallevels of said signal processor channels to said video amplifier meansin accordance with a predetermined program.
 4. A sonar system as definedin claim 1 and wherein: said peak detect and hold means of each signalprocessor channel comprises an operational amplifier, capacitor, anddiode combination, wherein the peak input signal is stored on saidcapacitor, and transistor means for discharging said capacitor to resetsaid peak detect and hold means; and said function generator meanscomprises means for generating a reset pulse following each of saidclock pulses, said transistor means being rendered conductive by saidreset pulse.
 5. A sonar system as defined in claim 4, and wherein: saidsample and hold means of each signal processor circuit comprises aswitching transistor, capacitor, and operational amplifier combination,and buffer amplifier means coupling said peak detect and hold means tosaid sample and hold means; and said switching transistor beingoperative in response to said clock signals to apply the output of saidbuffer amplifier means to said capacitor and operational amplifier ofsaid sample and hold means.
 6. A sonar system as defined in claim 5, andwherein said display means comprises cathode ray tube means.
 7. A sonarsystem as defined in claim 6, and further comprising: video amplifiermeans for driving said cathode ray tube means; and multiplexer means,including logic means and multiplexer gate means responsive to saidlogic means, for coupling said output signal levels of said signalprocessor channels to said video amplifier means in accordance with apredetermined program.
 8. In an ultrasonic, image conversion sonarsystem of the type including a source of clock signals representing theend of one pulse project period and the start of another, a plurality oftransducers, and receiver means having a plurality of correspondingchannels for generating echo envelope signals, reduced bandwidth signalprocessing and display apparatus comprising: a plurality of echoenvelope peak detection and hoLding means for providing a peak voltagelevel representative of the peak return signal in each of said channelsduring a first predetermined period in which echoes may be received froma given pulse transmission, said peak detection and holding means eachcomprising a storage capacitor connected to receive and store said peakvoltage level and transistor means connected to said capacitor fordischarging thereof in response to reset signals; reset signalgenerating means connected to said transistor means and responsive tosaid clock signals for generating said reset signals; a plurality ofsample and hold means, each connected by a buffer amplifier means to oneof said peak detection and holding means, for sampling the voltage levelstored on said storage capacitors in response to said clock signals, andfor providing corresponding voltage levels for a second predeterminedperiod following said first predetermined period, said sample and holdmeans each comprising a switching transistor, capacitor, and operationalamplifier combination; cathode ray tube means for generating a visibledisplay of said peak return signals; sweep generating means, connectedto said cathode ray tube means, for causing a raster to be tracedthereby; video amplifier means connected to the cathode of said cathoderay tube means and responsive to said corresponding voltage levels fromsaid sample and hold means, when applied thereto, to modulate theintensity of said visible display; and multiplexer means, includinglogic means and multiplexer gate means, said multiplexer means beingconnected between said sample and hold means and said video amplifiermeans so as to apply said corresponding voltage levels to said videoamplifier means in accordance with a predetermined program.